Four-point Probe Technique Research Articles

Acidic Derivatives of Melamine as Template in Copolymerization of Aniline and Metanilic Acid

ABSTRACTIn this paper, new polymer composites were synthesized by template copolymerization of aniline and metanilic acid in the presence of prepared melamine triacetic acid and poly(melamine-co-citric acid) as polyacids and dopants. The properties of the poly(aniline-co-metanilic acid) composites were studied by Fourier transform infrared, X-ray diffraction, scanning electron microscope, CV, and differential scanning calorimeter analysis. The four-point probe technique was used for evaluating the electrical conductivity of the composites. The scanning electron micrographs disclosed that the products had the morphology with agglomerated distorted spherical shapes with the average size of 40–50 nm. Also, the solubility of the composites had been improved notably in organic solvents.

Effect of organic solvents on the properties of DWCNT/PEDOT:PSS transparent conductive films

In this study, the transparent conductive films (TCFs) based on double-walled carbon nanotube (DWCNT) and poly (3,4-ethylene dioxythiophene): poly (styrene sulfonate) (PEDOT:PSS) were fabricated on glass substrates by spin coating method at room temperature. The DWCNTs with COOH functional group were dispersed in three different organic solvents including acetone, isopropanol and ethanol. The effect of organic solvents on the surface morphology, optical transmittance and sheet resistance of the DWCNT/PEDOT:PSS films were characterized by using the field emission scanning electron microscopy (FESEM), UV–vis spectroscopy and four-point probe technique. The results showed that the DWCNT/PEDOT:PSS films with the DWCNT-COOH dispersed in ethanol solvent had high transmittance of 80.3% at the 550 nm wavelength, low sheet resistance of 14.5 Ω/□ and figure of merit of 7.69 × 10−3 Ω−1. To evaluate the potential working performance in the photovoltaic devices, the prepared TCFs were used as a top electrode of the simple solar cell device based organic/inorganic (PEDOT:PSS/n-Si) hybrid structure. The highest power conversation efficiency (PCE) was obtained to be 5.35% for a cell using ethanol, which was about 2.3 and 1.4 times higher than that of cells using IPA and acetone as dispersion solvents for DWCNTs, respectively.

Multiscale modeling of the anisotropic electrical conductivity of architectured and nanostructured Cu-Nb composite wires and experimental comparison

Nanostructured and architectured copper niobium composite wires are excellent candidates for the generation of intense pulsed magnetic fields (> 90T) as they combine both high electrical conductivity and high strength. Multi-scaled Cu-Nb wires can be fabricated by accumulative drawing and bundling (a severe plastic deformation technique), leading to a multiscale, architectured and nanostructured microstructure providing a unique set of properties. This work presents a comprehensive multiscale study to predict the anisotropic effective electrical conductivity based on material nanostructure and architecture. Two homogenization methods are applied: a mean-field theory and a full-field approach. The size effect associated with the microstructure refinement is taken into account in the definition of the conductivity of each component in the composites. The multiscale character of the material is then accounted for through an iterative process. Both methods show excellent agreement with each other. The results are further compared, for the first time, with experimental data obtained by the four-point probe technique, and also show excellent agreement. Finally, the qualitative and quantitative understanding provided by these models demonstrates that the microstructure of Cu-Nb wires has a significant effect on the electrical conductivity.

The Effect of Substrate on Structural and Electrical Properties of Cu3N Thin Film by DC Reactive Magnetron Sputtering

The aim of this paper is to study the effect of substrate on the Cu3N thin films. At first Cu3N thin films are prepared using DC magnetron sputtering system. Then structural properties, surface roughness, and electrical resistance are studied using X-ray diffraction (XRD), the atomic force microscope (AFM) and four-point probe techniques respectively. Finally, the results are investigated and compared for glass and Si substrate. The results show a phase transition in orientation from (111) and (100) planes to (200) plane when the substrate of the sample is changed from glass to Si. Also, the grain size of deposited particles on films increased, changing substrate from glass to Si. Then, AFM results show that surface roughness on Si substrate is more than the glass substrate. Finally, four-point probe techniques show that surface electrical resistivity is increased sharply, changing substrate from silicon to glass.

In situ resistance measurements during physical vapor deposition of ultrathin metal films on Si(111) at room temperature

The resistance of ultrathin metal films (Ag, Au, Cr, Ir, Pt, and Ti) on hydrofluoric acid-treated Si(111) surfaces is investigated during room temperature evaporation at very low deposition rates (0.003–0.006 nm/s). High-resolution in situ measurements are performed using the four-point probe technique. The authors find that, in addition to the type of metal, the resistance versus metal thickness characteristics heavily depend on the doping of the Si substrate. Furthermore, for most metals on p-type Si, the resistance initially increases as a function of deposition time. The authors explain this by a conductive path at the surface due to H-terminated Si bonds which are destroyed during deposition.

Reaction conditions, photophysical, electrochemical, conductivity, and thermal properties of polyazomethines

In this paper, a series of Schiff bases and their polyazomethine derivatives were synthesized via condensation and oxidative polycondensation reactions of 4-aminophenol with 4-isopropylbenzaldehyde or 4-t-butylbenzaldehyde. Polymerization reaction conditions for polymerization yield of polyazomethines were investigated by changing some experimental parameters such as time and temperature using different oxidants like alkaline NaOCl (30%) and air. The structural characterizations of Schiff bases and polymers were performed using FT-IR, 1H NMR, 13C NMR and SEC techniques. Photophysical properties were studied UV-vis and photoluminescence spectroscopies. Electrochemical properties were also investigated cyclic voltammetry (CV) and electrochemical band gaps determined in the range 1.73 to 2.63 eV. Thermal properties of the compounds were investigated using TG-DTA and DSC techniques and char residue at 1000 oC determined between 3-6% and 39-34% for Schiff bases and polyazomethines, respectively. Moreover, conductivity measurements were done using four-point probe technique at both doped with iodine vapor and un-doped state.

Oxidative polycondensation of benzimidazole using NaOCl: Synthesis, characterization, optical, thermal and electrical properties of polybenzimidazoles

A series of polybenzimidazole polymers, poly-2-(1H-benzo[d] imidazole-2-yl) phenol (PBIP2), poly-3-(1H-benzo[d] imidazole-2-yl) phenol (PBIP3) and poly-4-(1H-benzo[d] imidazole-2-yl) phenol (PBIP4) were synthesized by oxidative polycondensation of benzimidazole monomers 2-(1H-benzo [d] imidazole-2-yl) phenol (BIP2), 3-(1H-benzo [d] imidazole-2-yl) phenol (BIP3) and 4-(1H-benzo [d] imidazole-2-yl) phenol (BIP4). The structure of benzimidazoles monomers and polybenzimidazoles (PBI) were confirmed by various spectroscopic techniques. The quantum theoretical calculations of band gap energy values of monomers were done with DFT and are compared with its optical band gap energy values. Fluorescence spectra of these compounds showed maximum emission in blue region. The electrical conductivity of PBIs was measured by four-point probe technique and showed good electrical response on iodine doping and conductivity increases with increase iodine doping time. The differences in conductivities among the three PBIs are in accordance with the charge density on imidazole nitrogens calculated by Huckel method. The high carbines residue (∼40%) at 500 °C in thermo gravimetric analysis shows that the PBIs are having reasonably good thermal stability. Polymers have recorded high dielectric constant at low applied frequency of 50 Hz at 393 K. The I–V characteristics of polybenzimidazoles p-n diodes showed rectifying nature with a typical forward to reverse current in the range −4 to 4 V. The high n values are caused by non homogeneities and effect of series resistance.

Polyaniline and carbon nanotube coated pineapple-polyester blended fabric composites as electrodes for supercapacitors

Conducting and electroactive fabrics suitable for supercapacitor electrodes were successfully prepared by combining carbon nanotubes (CNT) and polyaniline (PANi) with pineapple-polyester blended woven fabrics (PPWF) via dip-and-dry process and in situ chemical polymerization. The conductivity and capacitive behavior were studied using four-point probe technique, electrochemical impedance spectroscopy, cyclic voltammetry, and galvanostatic charge discharge experiments. PANi/CNT/PPWF composites produced higher conductivity (0.3877Scm−1) and areal capacitance values (386mFcm−2 at 1mAcm−2) compared to the binary composites, PANi/PPWF (0.00685Scm−1, 14.3mFcm−2), and CNT/PPWF (0.2615Scm−1, 8.52mFcm−2). Combining the high conductivity of CNT and the pseudocapacitive behavior of PANi greatly enhanced the charge storage capability of the composites. The PPWF composites also produced higher areal capacitance values compared to pure polyester composites. The incorporation of hydrophilic pineapple fibers led to lower charge transfer resistance and better electrolyte transport within the composite. Based on these characteristics, PANi/CNT/PPWF is a promising electrode material for supercapacitors.

Virtual substrate method for nanomaterials characterization

Characterization techniques available for bulk or thin-film solid-state materials have been extended to substrate-supported nanomaterials, but generally non-quantitatively. This is because the nanomaterial signals are inevitably buried in the signals from the underlying substrate in common reflection-configuration techniques. Here, we propose a virtual substrate method, inspired by the four-point probe technique for resistance measurement as well as the chop-nod method in infrared astronomy, to characterize nanomaterials without the influence of underlying substrate signals from four interrelated measurements. By implementing this method in secondary electron (SE) microscopy, a SE spectrum (white electrons) associated with the reflectivity difference between two different substrates can be tracked and controlled. The SE spectrum is used to quantitatively investigate the covering nanomaterial based on subtle changes in the transmission of the nanomaterial with high efficiency rivalling that of conventional core-level electrons. The virtual substrate method represents a benchmark for surface analysis to provide ‘free-standing’ information about supported nanomaterials.

The Effect of Sintering Temperature on The Rolled Silver-Sheathed Monofilament Bi,Pb-Sr-Ca-Cu-O Superconducting Wire

The manufacture of high critical temperature (Tc) Bi, Pb-Sr-Ca-Cu-O (HTS BPSCCO) superconductor wire fabricated by power-in-tube (PIT) is a multi-step process. The main difficulty is that the value of Tc superconductor wire determined by various factors for each step. The objective of this research is to investigate the effect of sintering parameters on the properties of final rolled material. The fabrication process of 1 m rolled-silver sheath monofilament superconductor BPSCCO wire using mechanical deformation process including rolling and drawing has been carried out. The pure silver powders were melted and formed into pure silver (Ag) tube. The tube was 10 mm in diameter with a sheath material: superconductor powders ratio of about 6 : 1. Starting powders, containing the nominal composition of Bi2-Sr2-Cam-1-Cum-Oy, were inserted into the pure silver tube and rolled until it reached a diameter of 4 mm. A typical area reduction ratio of about 5% per step has been proposed to prevent microcracking during the cold-drawing process. The process of rolling of the silver tube was subsequently repeated to obtain three samples and then followed by heat-treated at 820 °C, 840 °C, and 860 °C, respectively. The surface morphology was analyzed by using SEM; the crystal structure was studied by using X-RD, whereas the superconductivity was investigated by using temperature dependence resistivity measurement by using four-point probe technique. SEM images showed the porosity of the cross-sectional surface of the samples. The sample with low heating temperature showed porosity more than the one with high temperature. The value of critical temperature (Tc) of the sample with a dwelling time of heating of 8 hours is 70 K. At above 70 K, it shows the behavior of conductor properties. However, the porosity increased as the heating time increased up to 24 hours. The critical temperature was difficult to be identified due to its porosity. According to XRD results, the Bi-2212 phase is prominent in all samples.

STRUCTURAL, SURFACE AND TRANSPORT PROPERTIES OF Sn–Ag ALLOYS

The structural, surface and transport properties of Sn–Ag alloys were investigated by X-ray diffraction (XRD), radial heat flow, energy-dispersive X-ray (EDX) analysis, scanning electron microscopy (SEM) and four-point probe techniques. We observed that the samples had tetragonal crystal symmetry except for the pure Ag sample which had cubic crystal symmetry, and with the addition of Ag the cell parameters increased slightly. Smooth surfaces with a clear grain boundary for the samples were shown on the SEM micrographs. The grain sizes of pure Ag, [Formula: see text]-Sn and the formed Ag3Sn intermetallic compound phase for Sn–[Formula: see text] wt.% Ag [[Formula: see text], 3.5] binary alloys were determined to be 316[Formula: see text]nm, between 92[Formula: see text]nm and 80[Formula: see text]nm and between 36[Formula: see text]nm and 34[Formula: see text]nm, respectively. The values of electrical resistivity for pure Sn, pure Ag and Sn–[Formula: see text] wt.% Ag [[Formula: see text], 3.5] were obtained to be [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text][Formula: see text][Formula: see text]m at the temperature range of 300–450[Formula: see text]K, respectively. Thermal conductivity values of pure Sn and Sn–[Formula: see text] wt.% Ag [[Formula: see text], 3.5] binary alloys were found to be 60.60[Formula: see text]3.75, 69.00[Formula: see text]4.27 and 84.60[Formula: see text]5.24[Formula: see text]W/Km. These values slightly decreased with increasing temperature and increase with increasing of the Ag composition. Additionally, the temperature coefficients of thermal conductivity and electrical resistivity and the Lorenz numbers were calculated.

The thermoelectric power of Al-0.99 wt.% Fe alloys in the AC magnetic field

The melt structure of Al-0.99 wt.% Fe alloys in the AC magnetic field have been studied with thermoelectric power by the four-point probe technique and microstructure with the liquid quenching method. The melt temperature is in the range of 913 K–1013 K. The thermoelectric power increases due to the AC magnetic field and decreases after the AC magnetic field stops, then keeps stable. Some characteristic parameters of thermoelectric power in the recovery process are used to represent the variation of melt structure. The α-Al phase refinement in the AC magnetic field is attributed to the persistent variation of melt structure. The persistent variation of thermoelectric power can be used to characterize the variation of the α-Al phase size. The hardness increases and the diffraction peaks of some planes reduce, which can reflect the uniform and disorder melt structure in the AC magnetic field.

Microstructural, mechanical, electrical, and thermal properties of the Bi-Sn-Ag ternary eutectic alloy

The development of lead-free solders has emerged as one of the key issues in the electronics packaging industries. Bi-Sn-Ag eutectic alloy has been considered as one of the lead-free solder materials that can replace the toxic Pb-Sn eutectic solder without increasing soldering temperature. We investigated the effects of temperature gradient and growth rate on the mechanical, electrical and thermal properties of the Bi-Sn-Ag ternary eutectic alloy. Bi-47 wt%Sn-0.68 wt%Ag alloy was directionally solidified upward with different temperature gradients (G=2.33-5.66 K/mm) at a constant growth rate (V=13.25 μm/s) and with different growth rates (V=6.55-132.83 μm/s) at a constant temperature gradient (G=2.33 K/mm) in the growth apparatus. The microstructures (λ), microhardness (HV), tensile stress (σ), electrical resistivity (ρ), and thermal properties (ΔH, C p, T m) were measured on directionally solidified samples. The dependency of the λ, HV, σ, and ρ on G and V was investigated. According to the experimental results, λ values decrease with increasing G and V, but HV, λ, and ρ values increase with increasing G and V. Variations of electrical resistivity (ρ) for cast samples with the temperature in the range of 300-400 K were also measured by using a standard dc four-point probe technique. The enthalpy of fusion (ΔH) and specific heat (C p) for the same alloy was also determined by means of differential scanning calorimeter (DSC) from heating trace during the transformation from eutectic liquid to eutectic solid.

Synthesis, characterization and electrochemical properties of poly(phenoxy-imine)s containing carbazole unit

Several new Schiff base polymers were synthesized via oxidative polymerization method in an aqueous alkaline medium in the presence of NaOCl as an oxidant and were confirmed by FT-IR, 1H-NMR, 13C-NMR and UV–Vis spectroscopic techniques. Furthermore, cyclic voltammetry measurements were carried out and the HOMO–LUMO energy levels and electrochemical band gaps (Eg′) were calculated. Additionally, the optical band gaps (Eg) were determined using their UV–Vis spectra of the materials. The morphologic properties of the polymers were investigated by scanning electron microscopy. In addition, the number average molecular weight (Mn), weight average molecular weight (Mw) and polydispersity index values of the polymers were determined by gel permeation chromatography technique. Electrical conductivity measurements of the doped (with iodine) and undoped polymer related to doping time were carried out by four-point probe technique using a Keithley 2400 electrometer. Their thermal behaviors were determined by TG–DTA and DSC measurements. The synthesized compounds were soluble in common solvents such as DMF, THF and DMSO. Photoluminescence properties of the polymers were determined in different concentrations of DMF solvent.

Synthesis and Characterizations of Poly(phenoxy-Imine)s via Catalyzed Oxidative Polymerization by Polymer–Metal Complex

In this study, Schiff base was synthesized from the condensation reaction of 3,5-diaminobenzoic acid, 4,4\(^\prime \)-diaminobenzanilide, vanillin with 4-hydroxybenzaldehyde. Then, Schiff bases polymers were synthesized via oxidative polycondensation method in the presence of catalyst (polymer–metal complex) in organic solvent. Schiff base polymers were compared to the ones which were previously polymerized without catalyst. The structures of synthesized monomers and polymers were determined by FT-IR, NMR, SEC and SEM analyses; the optical characteristics by UV–Vis and fluorescence spectroscopy methods, solid state conductivity measurements by four-point probe technique, the electrochemical properties by CV analysis, thermal behaviors by TG-DTA and DSC measurements were effectively determined. Depending on the synthetic method of polymer, structural change, optical, electrochemical and thermal differences were measured. Availability of these polymers in the production of light-emitting diode, electronic–optoelectronic and thermal resistant materials was explored.

Surface Morphology and Electrical Resistivity in Polycrystalline Au/Cu/Si(100) System

This work describes the analysis of morphology and electrical resistivity (ρ) obtained in the Au/Cu/Si system. The Au/Cu bilayers were deposited by thermal evaporation technique with thicknesses from 50 to 250 nm on SiOx/Si(100) substrates. The Au : Cu concentration ratio of the samples was of 25 : 75 at%. The bilayers were annealed into a vacuum oven with argon atmosphere at 660 K for one hour. The crystalline structures of AuCu and CuSi alloys were confirmed by X-ray diffraction analysis. The scanning electron microscopy (SEM), the atomic force microscopy (AFM), and the energy dispersive spectroscopy (EDS) were used to study the morphology, final thickness, and the atomic concentration of the alloys formed, respectively. The four-point probe technique was used to measure the electrical resistivity (ρ) in the prepared alloys as a function of thickness. The ρ value was measured and it was numerically compared with the Fuchs–Sondheimer (FS) and the Mayadas–Shatzkes (MS) models of resistivity. Results show values of electrical resistivity between 0.9 and 1.9 μΩ-cm. These values are four times smaller than the values of the AuCu systems reported in literature.

Improvement of electrochemical and structural properties of polycarbazole by simultaneous electrodeposition of chitosan

Polycarbazole/chitosan composite materials were synthesized electrochemically at various loadings of chitosan (Chi). Their electrochemical, structural, thermal, and morphological characterizations were investigated by cyclic voltammetry, chronoamperometry, electrochemical impedance spectroscopy, Fourier transform infrared spectroscopy, thermal gravimetry, and scanning electron microscopy. Further electrical conductivity was measured using a four-point probe technique. The electrochemical results showed that the electrical conductivity of the polymeric composite film was increased by increasing the amount of Chi in the electrolyte medium. The as-prepared composite films exhibited enhanced electrical conductivity and structural properties of polycarbazole due to the presence of Chi in the composite films.

Theory and verification of a microwave transmission method of measuring sheet resistance of metallic thin film

Metallic thin films deposited on non-conductive substrates are widely used in areas like microwave absorbers, photovoltaic, packaging, electromagnetic shielding, and integrated circuits. From scientific and engineering point of view, measuring sheet resistance of metallic thin films is important. In this study, we develop a theory of evaluating sheet resistance by using transmission coefficient of a rectangular waveguide (RG) and verify it with sputtered silver films of various thickness values. According to the field distribution of RG working under the fundamental mode and corresponding electromagnetic boundary conditions, we first analytically derive the transmission coefficient of an RG with the metallic thin film exactly occupying its cross section. Comparing existing theory, we take the effect of the non-conductive substrate supporting the metallic thin film into consideration. According to this derivation, we establish a method to calculate the sheet resistance of metallic thin films from the amplitude of RG transmission coefficient. To verify our derivation, we also conduct full-wave simulations of a standard WR-75 RG used for characterizing the metallic thin film at 13.65 GHz. Both the analytical derivations and full-wave simulations show that the amplitude of the transmission coefficient depends on the logarithm of the sheet resistance in a linear manner. It is also demonstrated that the substrate effect may not be ignored. To facilitate measurement, we propose a sandwiched structure by placing the metallic thin film between two waveguide flanges. This modification removes the stringent requirements for sample preparation. Simulations of this sandwiched structure indicate that it is possible to realize non-contact measurement if the air gap between metallic thin film and waveguide flange is below 0.1 mm. Through full-wave simulations, we also show the feasibility of metallic thin film evaluation by using such transmission lines as dielectric filled RG, circular waveguide, and coaxial line. Finally, we prepare various silver films with sheet resistances ranging from 20 m/square to 1 /square (measured by the four-point probe technique) on the top of high resistance silicon and glass substrates, respectively. We measure the amplitudes of transmission coefficient of these metal films in RG by using vector network analyzer. The obtained experimental results are well consistent with the derivation and simulation results, thereby verifying the proposed method. It is recommended that the proposed method is suitable for conductive films with sheet resistances ranging from 0.05 /square to 0.5 /square. The results of this study are of potential value for characterizing the conductive thin films in micro/nano fabrication and relevant areas.

Effect of CNTs and nano ZnO on physical and mechanical properties of polyaniline composites applicable in energy devices

Polyaniline was synthesized chemically in an acidic medium in the presence of Ammonium Peroxydisulphate (APS) as an oxidizing agent. PANI(Polyaniline) nanocomposites were prepared in the presence of various amount of carbon nanotube and zinc oxide (from 1 to 5wt%) by solution casting method. The free-standing film of polyaniline and its nanocomposites were obtained by vaporization of solvent content. The composition, morphology and structure of the polymer and the nanocomposites were characterized by Fourier transform infrared spectroscopy FT-IR spectra, scanning electron microscopy (SEM) image and XRD pattern. In addition, thermal stability was studied by TGA analysis, electrical conductivity was measured by four-point probe technique and mechanical properties were studied by tensile strength test. The characteristic FTIR peaks of PANI were found to shift to lower wave number in nanocomposites due to the formation of H-bonding. XRD results revealed that the crystallinity of PANI was more noticeable after addition of nano-ZnO, while the intensity of the peaks increased by the addition of ZnO nanoparticles. Furthermore, TGA results showed that the decomposition of the nanocomposite was less than that of pure polyaniline which confirms the successful fabrication of products. Young's modulus and strength at break point were increased in the case of the nanocomposite, in addition, the electrical conductivity of the PANI/ZnO nanocomposite film was found to be smaller than that of the PANI film while CNTs increase the conductivity of polyaniline.

Structural, electrical, and mechanical characterization of Al 5086 alloy irradiated with 248 nm–20 ns KrF excimer laser

Williamson-Hall analysis of XRD patterns of Al 5086 alloy specimens (10 mm × 10 mm × 6 mm) irradiated with 100–500 KrF excimer laser pulses in air (1 bar) as well as in vacuum (10−3 mbar) was done to evaluate structural changes on laser irradiation. Both crystallite size (30 nm–99 nm) and lattice strain (0.00043–0.00241) were found, in general, to increase with the number of laser shots first rapidly up to 200 and later on rather slowly. Also, for a given number of laser shots, the crystallite size of the specimen laser-irradiated in vacuum was higher than that of the specimens laser-irradiated in air. Harris analysis of XRD patterns revealed that the most preferentially oriented plane was (200) with texture coefficient in the range 2.359–2.982. Electrical resistivity of the specimens was measured by four-point probe technique. It was found to increase with the number of laser shots up to 200, and later on decreases monotonically. However, for a given number of laser shots, its value was higher for the specimen laser-irradiated in air than that for the specimen laser-irradiated in vacuum. On plotting combined surface hardness data for un-irradiated and laser-irradiated specimens in air as well as in vacuum as a function of inverse square-root of crystallite size, a cross over from classical Hall-Petch relation (99 nm–55 nm) to inverse Hall-Petch relation (55 nm–30 nm) occurred at about 55 nm. This is true not only for the surface hardness but also for the hardness measured at 0.5 and 1.0 mm depth below the specimen surface. The intensity of laser-hardening effect gradually diminishes as one goes down from the uniformly laser-irradiated specimen surface to a depth of 3.0 mm below it. The relationship between electrical resistivity and surface hardness was linear.